Railway track circuit apparatus



July 25, 1967 J. E. OHMAN ET AL RAILWAY TRACK CIRCUIT APPARATUS Filed April 5, 1964 l 9 s V 33 i2 v' S I ,2 i I r I I A I I 2 I i? I 6 I I3 '2 ML -Il I WARNING 2a 4 SIGNAL 7 1:

POWER SUPPLY OSCILLATOR M I IAMPLIFIER 2 2| I87 RECEIVER RECEIVER RECEIVER I I 25 24 23 I I 1 J I I LEFT ISLAND RIGHT I RELAY RELAY RELAY I I II A I j I I I I L I I INTERLOCKING INTERLOCKING I I RELAY 2? RELAY 26 I I I 4 J I I J JERALD E. OHMAN CROSSWG 32 RELAY INVENTORS BY MALI ATTORNEY United States Patent 3,333,096 RAILWAY TRACK CIRCUIT APPARATUS Jerald E. Ohman, Claremont, and Robert J. Marks, Westminster, Caliil, assignors to The Marquardt Corporation, Pomona, Calif., a corporation of California Filed Apr. 3, 1964, Ser. No. 357,126 4 Claims. (Cl. 246-34) This invention relates to railroad track circuits and more particularly to an electronic track circuit which detects the presence of a train at a given track location for activating crossing protection devices or for providing block signals, and which does not require insulated track joints.

Many devices have been constructed heretofore which would detect the presence of a train at a given track location. For various reasons, the apparatus used most generally has necessitated the electrical isolation of a track section by means of insulated rail joints. While overcoming most of the undesirable features of other techniques, insulated rail joints are relatively difficult and costly to install and maintain. In addition to the difficulty and expense entailed in the installation of insulated joints, their reliability is subject to degradation by environmental conditions thus comprising the safety of the railway. By the present invention means are provided for detecting the presence of a train without the necessity of insulating sections of the tracks. The novel apparatus of the invention is applicable to electrified as well as diesel railways. Also, the apparatus of the invention provides a novel and simplified approach to railroad track circuits. All active functions are performed from a single location without the necessity of insulated joints and operation is reliable in low temperature, low ballast, and long distance situations such as would adversely afiect prior devices intended to accomplish generally similar results. The present invention transmits an AC signal through the rails and continuously monitors the impedance of the track circuit. As a train crosses the signal feed point the track impedance is greatly lowered due to the shunting of the rails by the train wheels and axles. A detector circuit is responsive to this impedance change to energize a control relay, which in turn may operate any desired external utilization circuit such as a block signal circuit. 'While the device does not provide a signal which is as precisely timed as may be obtained from a mechanically actuated track switch, it will nonetheless give a highly reliable signal which meets practical requirements as to timing accuracy. Furthermore, the device is responsive to the direction of train movement to provide corresponding output signals. In many railroad signal systems there is no requirement for precise timing of signal activation.

A feature of the present invention is its employment of the principal of current division whereby impedance changes either to the right or left of the rail feed point will activate the device and thus provide a simple reliable system for protecting crossings and for providing block signals without the necessity of insulated rail joints.

An object of this invention is to provide a novel and improved railway track circuit which is responsive to the presence of a train to control ancillary devices.

Yet another object of this invention is the provision of a unique railway track circuit which is more inexpensive to install and maintain than devices employed heretofore to accomplish generally similar results.

Still another object of the present invention is the provision of a railway track circuit which is completely reliable.

It is yet another object of the invention to provide a novel and improved railway track circuit such as may be used to generate block signals which obviates mechanically actuated switch mechanisms as well as insulated track joints.

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It is still another object of the present invention to provide a novel and improved railway track circuit which is capable of indicating both the direction of approach and arrival of a train at a specified track site.

A general object of this invention is to provide novel and improved railway track circuit apparatus which overcomes disadvantages of previous means and methods heretofore intended to accomplish generally similar purposes.

These and other objects of the present invention are achieved in an arrangement wherein the railroad track is considered as a shorted transmission line in which the short is provided by the wheels and axle of the train. An alternating-current signal with a substantially constantcurrent level is applied to the tracks at the location from which the track signal is to be generated. The voltage existing across the tracks will diminish as the shorting wheels and axle of the train approaches the energized section of track. The downward change in this voltage level is detected and ultimately used to operate a relay having suitable switching contacts for performing any desired switching functions. Since the excitation current is divided between the right and left directions, by sensing impedance changes on either side of the feed point, direction of approach of the train may be indicated.

The invention resides primarily in the inter-relationships of the circuit components of the system and embraces the concept of the system itself, considered as an integrated whole, and independently of the structural details of its several parts.

The novel features that are characteristic of this invention are set forth with particularity in the appended claims. The invention itself, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawing.

Looking at the drawing there is shown a block diagram of a preferred embodiment of the invention such as may be used in a railroad grade crossing protection system. Oscillator 1 furnishes a signal at a suitable frequency to constant current power amplifier 2 which excites the rails 3 and 4 at feed points 5 and 6 through a narrow-band series-resonant filter 7. Power is supplied from source 8. The series resonant filter 7 is a passive inductance capacity combination tuned to the frequency of the signal from oscillator 1. The filter 7 offers a low impedance at the transmitted frequency and a progressively higher impedance as the frequency increases or decreases. The filter also provides a low resistive component resulting in less power dissipation in the driving circuit and consequently less current required from the power supply 8. Furthermore, filter 7 serves as an isolation to the power amplifier 2 when a train is shorting the rails at feed points 5 and 6, and for other signal frequencies which may be in the rails.

Inasmuch as each of the functional units represented by a rectangle or block in the drawing may be any one of the numerous devices for each respective function well known in the art it is deemed unnecessary to show circuit details. The oscillator, amplifier, and other functional units may be transistorized, as will be apparent to those skilled in the art, and it is believed that the description which follows is sufficient to enable the invention to be practiced. Initially, the coaction of the system components will be described in a general Way, and thereafter, specific details of the systems operation will be described.

The current from amplifier 2, which excites rails 3 and 4, at feed points 5 and 6, is divided between the right and left directions. This current, after passing through the rails, which act as bare wire transmission lines, develops a voltage across inductance coils 11 and 12. This voltage is proportional to the current in coils 11 and 12, which with capacitors 13 and 14 form left and right narrow band A-C shunts, tuned to resonance at the excitation frequency. The signal voltages developed across the coils 11 and 12 are carried by wire pairs 15 and 16 to receivers 17 and 18, respectively. The voltage at points and 6 is carried by line wire pair 19 to receiver 21. The voltage in wire pair 19 is proportional to the impedance of rails 3 and 4 and the right and left A-C shunts. The voltage output of the receivers 17, 18, and 21 control the operation of crossing relay 22 through right relay 23, island relay 24, left relay 25, and interlocking relays 26 and 27. Crossing relay 22 controls the operation of warning signal28.

As can be seen, there are three separate signal pickoif points on the transmission line, one of which is coincident with the excitation point. In operation, with no train approaching, oscillator 1 provides a continuous output signal to nails 3 and 4 through amplifier 2. Consequently, a signal voltage is continuously developed across coils ll and 12 and at points 5 and 6. This voltage, applied through receivers 17, 18, and 21, is of suflicient magnitude to keep control relays 23, 24, and 25 energized. In this condition, crossing relay 22 is also energized and warning signal 28 is inactive. Receivers 17, 18, and 21 each may comprise any suitable and Well-known A-C voltage detector which is responsive to the presence of an A-C signal of appropriate frequency and amplitude to provide an output control signal capable of energizing a relay.

When a train approaches the crossing in a direction from right to left, as viewed in the drawing, part of the current, which has been flowing through coil 12, is now diverted through the train wheels and axles. Thus, the voltage which is developed in cross coil 12 is transmitted to receiver 18, decreases as the train approaches points 33-34. When the train reaches the close proximity of points 33-34, the voltage of cross coil 12 will have been reduced sufficiently that relay 23 is de-energized and crossing relay 22 operates to activate the warning signal 28.

As the train crosses points 33-34 and approaches crossing 9, the voltage developed at points 5 and 6 decreases due to the lowered impedance in the track circuit caused by the moving train. This voltage is representative of the distance between the train and points 5 and 6. It will be appreciated that as the train approaches the feed point on the tracks to which current from the constant current generator is applied, the impedance of the track looking toward the train from the feed point is continuously being diminished. This follows by reason of the fact that the train comprises a short across the tracks which is moved toward the points 5 and 6. With current being maintained constant, the voltage at the points 5 and 6 will continuously decrease to zero when the train reaches the points '5 and 6. Therefore, by detecting when the voltage across the tracks reaches a specified minimum .an infor a train moving right to left, island relay 24 must also dication is obtained of the presence of a train at the close proximity of the crossing 9. When the train reaches the points 5 and 6, the signal voltage to receiver 21 has become low enough to cause island relay 24 to de-energize. At approximately the same time, suflicient current is diverted from the left A-C shunt through the train to cause the voltage signal at receiver 17 to decrease sufliciently in amplitude to de-energize left relay 25.

As the rear endof the train leaves crossing 9, the signal voltages at receivers 18 and 21 will have increased sufliciently to energize relays 23 and 24, respectively, and thus inactivate warning signal 28 by energizing the crossing relay 22 through the interlocking relay 26. Left relay 25 is energized again when the rear of the train passes points 31-32 and sutficient voltage is again developed across coil 11.

Interlocking relays 26 and 27 are used to give train direction controls to the warning system. When right relay 23 is ,de-energized, a back contact energizes interlockbe de-energized before interlocking relay 27 can be energized, in order to provide continuous protection.

The description given hereinabove illustrates the systems operation for a train moving from right to left. For a train moving from left to right, the operation is essentially the same but in reverse order.

While the above-described embodiment of the invention has been discussed in terms of its application to a crossing warning device, 'it should be understood that any desired utilization apparatus may be substituted for warning signal 28, as for example a conventional block signal relay.

Since the system is responsive to a diminution of signal voltage to indicate the presence of a train, it is essentially fail-safe since an open track bond or similar defect would cause cessation of the signal and thus activate the control relays.

Various circuits have been represented herein by blocks bearing the functional designation. These individual circuits are all well known in the electronic field, being amply described in the literature and for the most part commercially purchasable as individual components from several manufacturers, either using vacuum tubes or transistors. Accordingly, detailed descriptions of these circuits are omitted, since this would only add to the complexity of the description without adding any further understanding of the invention.

Accordingly, there has been described and shown herein a novel and useful track circuit signal system which actuates warning devices or other utilization apparatus from information as to the presence of a train in a designated section of track and which is derived from the track without the necessity of insulated joints.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art, without departing from the spirit of the invention; therefore, it is intended that the invention be limited only as indicated by the scope of the following claims.

What is claimed is:

1. Railway track circuit apparatus for detecting the presence of a train at a given site on a two-rail railroad, comprising:

excitation means for applying a constant-current A-C signal across the rails of said'railroad at said site;

a first receiver means connected across said rails at said site and responsive to changes in the voltage amplitude of said A-C signal to generate a first control signal;

an island relay connected to said first receiver means and adapted to be activated by diminution of said first control signal;

a second receiver means connected across said rails at a location spaced apart fromsaid site and responsive to changes in the voltage amplitude of said A-C signal to generate a second control signal;

a first control relay connected to said second receiver means and adapted to be activated by diminution of said second control signal;

a third receiver means connected across said rails at a location spaced apart from said side in a direction along said rails opposite the location of said second receiver connection, and responsive to changes in the voltage amplitude of said A-C signal to generate a third control signal;

a second control relay connected to said third receiver means and adapted to be activated by diminution of said third control signal; and

means responsive to activation of said first and second control relays and said island relay to indicate the direction of approach, and the presence of said train, at said site.

2. Railway track apparatus as defined in claim 1 wherein said activation responsive means includes:

first and second interlocking relay means for continuously activating a utilization circuit until cessation of at least two of said three control signals, due to said train leaving said site.

3. Railway track apparatus as defined in claim 2 wherein said utilization circuit includes:

a crossing relay connected to said first and second interlocking relay means; and

a warning signal device connected to said crossing relay, whereby said iwarning signal device is continuously activated while said train is at either of said locations or said site.

4. Railway track circuit apparatus comprising:

a fixed-frequency constant-current signal generating means for exciting a pair of track rails;

island detector means tuned to said fixed-frequency and connected across said rails, whereby changes in impedance resulting from the shorting of said rails by a train will produce an island control signal;

first receiver means connected across said rails at a point spaced apart from the point of connection of said island detector means in a first direction, said first receiver means being tuned to said fixed-frequency and being responsive to changes in track impedance resulting from the shorting of said rails by .a train to produce a first control signal;

second receiver means connected across said rails at a point spaced apart from the point of connection of said island detector means, and at a location opposite the point of connection of said first receiver means, said second receiver means being tuned to said fixed-frequency and being responsive to changes in track impedance resulting from the shorting of said rails by a train to produce a second control signal; and

first and second interlocking relay means connected to said island detector means and to said first and second receiver means, and responsive to diminution of said island control signal and said first and second control signals, to indicate the direction of approach and the presence of said train at said point of connection of said island detector means.

References Cited UNITED STATES PATENTS 2,186,201 1/ 1940 McFarland 24634 2,790,895 4/ 1957 Schaefer 2461'30 2,930,888 3/ 1960 Crawford et a1 246124 2,993,116 7/1961 Utt- 24634 3,035,167 5/1962 Luft 24634 X 3,069,542 12/1962 Failor 24633 3,155,350 11/1964 Campbell 246-122 3,246,143 4/1966 Steele et a1. 246l30X ARTHUR L. LA POINT, Primary Examiner.

S. B. GREEN, S. T. KRAWCZEWICZ,

Assistant Examiners. 

1. RAILWAY TRACK CIRCUIT APPARATUS FOR DETECTING THE PRESENCE OF A TRAIN AT A GIVEN SITE ON A TWO-RAIL RAILROAD, COMPRISING: EXCITATION MEANS FOR APPLYING A CONSTANT-CURRENT A-C SIGNAL ACROSS THE RAILS OF SAID RAILROAD AT SAID SITE; A FIRST RECEIVER MEANS CONNECTED ACROSS SAID RAILS AT SAID SITE AND RESPONSIVE TO CHANGES IN THE VOLTAGE AMPLITUDE OF SAID A-C SIGNAL TO GENERATE A FIRST CONTROL SIGNAL; AN ISLAND RELAY CONNECTED TO SAID FIRST RECEIVER MEANS AND ADAPTED TO BE ACTIVATED BY DIMINUTION OF SAID FIRST CONTROL SIGNAL; A SECOND RECEIVER MEANS CONNECTED ACROSS SAID RAILS AT A LOCATION SPACED APART FROM SAID SITE AND RESPONSIVE TO CHANGES IN THE VOLTAGE AMPLITUDE OF SAID A-C SIGNAL TO GENERATE A SECOND CONTROL SIGNAL; A FIRST CONTROL RELAY CONNECTED TO SAID SECOND RECEIVER MEANS AND ADAPTED TO BE ACTIVATED BY DIMINUTION OF SAID SECOND CONTROL SIGNAL; A THIRD RECEIVER MEANS CONNECTED ACROSS SAID RAILS AT A LOCATION SPACED APART FROM SAID SIDE IN A DIRECTION ALONG SAID RAILS OPPOSITE THE LOCATION OF SAID SECOND RECEIVER CONNECTION, AND RESPONSIVE TO CHANGES IN THE VOLTAGE AMPLITUDE OF SAID A-C SIGNAL TO GENERATE A THIRD CONTROL SIGNAL; A SECOND CONTROL RELAY CONNECTED TO SAID THIRD RECEIVER MEANS AND ADAPTED TO BE ACTIVATED BY DIMINUTION OF SAID THIRD CONTROL SIGNAL; AND MEANS RESPONSIVE TO ACTIVATION OF SAID FIRST AND SECOND CONTROL RELAYS AND SAID ISLAND RELAY TO INDICATE THE DIRECTION OF APPROACH, AND THE PRESENCE OF SAID TRAIN, AT SAID SITE. 